In recent years, battery systems equipped with secondary batteries such as lithium ion batteries are being used for a variety of purposes. Such battery systems are used for, for example, back-up power supply with the object of dealing with power outage of home electronics, outdoor stationary type power supply system for residences, auxiliary power supply in a factory or plant facility, and back-up power supply in office buildings. In addition, such battery systems are also used for power peak cutting and peak shifting with the object of using nighttime power and avoiding peak daytime power usage.
With the increasingly widespread use of the above-described battery systems has come the necessity not only for high capacity and high voltage, but also for high safety and economy.
To increase the capacity and voltage of a battery system, a multiplicity of secondary batteries are series-parallel connected. Providing both high safety and economy in a battery system of this type requires both the monitoring of the state of the multiplicity of batteries in the system as well as efficiently matching power requirements to be connected to the power supply (reducing the power consumption in the battery system).
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2011-109768) discloses a technology in a battery pack that is provided with a battery protection circuit that is shut down when the device that is to be charged/discharged is not connected to the battery pack.
In addition, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2008-125268) discloses a technology in a battery pack that is provided with a protection circuit that protects the battery in which the operating state of the protection circuit is transitioned to a reduced power consumption state when a command indicating a demand for information of the remaining capacity of the battery is not received from an outside apparatus.
According to the technology of Patent Document 1 and Patent Document 2, a reduction of the power consumption and an increase of economy can be achieved by shutting down the protection circuit or transitioning to a reduced power consumption.